Summary
Oxidative stress is associated with disease severity and limb muscle dysfunction in COPD. The main goal was to assess the effects of exercise training on systemic oxidative stress and limb muscle dysfunction in older people with COPD. Twenty-nine outpatients with COPD (66-90 years) were randomly assigned to a 12-week exercise training (ET; high-intensity interval training (HIIT) plus power training) or a control (CT; usual care) group. The variables evaluated were mid-thigh muscle cross-sectional area (CSA; computed tomography); vastus lateralis (VL) muscle thickness, pennation angle, and fascicle length (ultrasonography); peak VO2 uptake (VO2peak ) and work rate (Wpeak ) (incremental cardiopulmonary exercise test); rate of force development (RFD); maximal muscle power (Pmax ; force-velocity testing); systemic oxidative stress (plasma protein carbonylation); and physical performance and quality of life. ET subjects experienced changes in mid-thigh muscle CSA (+4%), VL muscle thickness (+11%) and pennation angle (+19%), VO2peak (+14%), Wpeak (+37%), RFD (+32% to 65%), Pmax (+38% to 51%), sit-to-stand time (-24%), and self-reported health status (+20%) (all P < 0.05). No changes were noted in the CT group (P > 0.05). Protein carbonylation decreased among ET subjects (-27%; P < 0.05), but not in the CT group (P > 0.05). Changes in protein carbonylation were associated with changes in muscle size and pennation angle (r = -0.44 to -0.57), exercise capacity (r = -0.46), muscle strength (r = -0.45), and sit-to-stand performance (r = 0.60) (all P < 0.05). The combination of HIIT and power training improved systemic oxidative stress and limb muscle dysfunction in older people with COPD. Changes in oxidative stress were associated with exercise-induced structural and functional adaptations.

Relevance
The identification of potential therapies targeting oxidative stress in people with COPD may be beneficial to prevent disease progression and other COPD‐related consequences. A recent study demonstrated the antioxidant benefits derived from exercise participation in people with COPD,30 but it remained unknown whether the absolute level of oxidative stress remained unchanged. Our findings add novel evidence on the benefits derived from concurrent exercise training on systemic oxidative stress in older people with COPD. Oxidative stress may play a role as a regulator of exercise‐ induced structural and functional adaptations in skeletal muscles of patients with COPD. In this regard, the effects of exercise training on oxidative stress in patients with COPD might be tightly regulated by exercise dosage, and thus, exercise programs should be carefully prescribed in sedentary older people with COPD in order to maximize their benefits. Future studies should be conducted in order to assess the dose‐response relationship between exercise training and oxidative stress in subjects with COPD, as well as the effect of adding power training to conventional pulmonary rehabilitation programs.